Glial fibrillary acidic protein promoter determines transgene expression in satellite glial cells following intraganglionic adeno‐associated virus delivery in adult rats

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Ganglionic satellite glial cells (SGCs) are an important element in the pain signaling pathways (Hanani, 2005; Scholz & Woolf, 2007). SGC proliferation and activation following nerve injury influences sensory processing by various mechanisms including alteration of gene expression; increased coupling between SGCs and between SGCs and neurons; and chemokine/cytokine release, which induces microglia activation (Liu & Yuan, 2014; McMahon & Malcangio, 2009; Milligan & Watkins, 2009; Watkins & Maier, 2003). Genetic manipulation of SGC‐specific molecules such as connexin 43 (Cx43) (Ohara, Vit, Bhargava, & Jasmin, 2008), glutamine synthase (GS) (Jasmin, Vit, Bhargava, & Ohara, 2010), ATP‐sensitive inward rectifier potassium channel 10 (Kir4.1) (Vit, Ohara, Bhargava, Kelley, & Jasmin, 2008), excitatory amino acid transporter 1 (EAAT1) (Jasmin et al., 2010), purinergic ionotropic P2X7 receptor (P2X7R) (Chen et al., 2008), and GFAP (Kim et al., 2009), can substantially alter sensory responses in normal and nerve‐injured rodents. Thus, therapeutic gene modulation specifically targeting the SGC population in dorsal root ganglia (DRG) could offer new opportunities for chronic pain treatment (Gao & Ji, 2010; Jasmin et al., 2010; McMahon & Malcangio, 2009).
Gene therapy has demonstrated a potential for novel treatments for chronic pain. In preclinical studies, gene delivery by use of adeno‐associated viral (AAV) has been established as an efficient tool for gene transfer into postmitotic peripheral sensory neurons and for long‐term control of neuropathic pain with minimal toxicity (Asokan, Schaffer, & Samulski, 2012; Beutler, 2010; Beutler & Reinhardt, 2009; Mason et al., 2010; Yu et al., 2013). The capsid protein and the promoter are major determinants of AAV tropism to different cell types. The natural tropism of AAV vectors based on the widely used AAV2 genome with constitutively active promoters and pseudotyped with various serotype capsids leads predominantly to neuronal transduction. Although variable, a low level of nonselective SGC transduction in vivo after intraganglionic delivery has been reported, and the use of AAV to transduce SGCs has generally resulted in limited success in adult animals (Asokan et al., 2012; Beutler, 2010; Beutler & Reinhardt, 2009; Mason et al., 2010; Yu et al., 2013). This view has been challenged in the central nervous system by showing that use of a GFAP promoter increases the astrocyte transduction of AAV‐mediated transgene expression (von Jonquieres et al., 2013). However, whether GFAP promoter determines glial cell transduction in DRG has not been reported. Capsid protein is another important determinant for AAV tropism. AAVshH10 (an AAV6 capsid variant) and AAVshH19 (an AAV2 capsid variant) are recently engineered novel AAV capsids that provide efficient Müller glia‐permissive gene expression (Dalkara et al., 2011; Klimczak, Koerber, Dalkara, Flannery, & Schaffer, 2009; Koerber et al., 2009; Zolotukhin et al., 2013). It is not clear, however, whether these AAV capsid mutants can be adopted for gene transfer to ganglionic SGCs.
The purpose of this study was to evaluate whether cell specificity for the SGC transduction in DRG could be enhanced using AAVshH10 and AAVshH19 capsids, and transgene‐driven by SGC‐specific GFAP promoter. Our work establishes that GFAP promoter is effective in providing SGC‐selective transgene expression following intraganglionic AAV delivery in adult rats, and this strategy should prove useful for the development of gene expression systems targeting SGC signaling for chronic pain.

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